Injectors or injection nozzles form significant components of an internal combustion engine. The injectors are used to inject fuel into respective cylinders before a fuel/air mixture is ignited by compression. Each injector is at least in most cases arranged in a respective recess provided in a cylinder head of the engine. Each injector includes a valve, which is opened for injection. This can be accomplished, on the one hand, by means of a pressure pulse produced by a pump associated with the individual injector. On the other hand, it is also possible for the valve to be controlled electromagnetically, wherein all of the injectors are supplied by a common pressure reservoir. Depending on the design of the engine, injection is performed directly into the combustion chamber (direct injection), wherein the piston top often has an annular recess, or alternatively into a swirl chamber of a split combustion chamber (chamber-type engine).
In addition to the geometry of the injector, in particular the number, shape, size and alignment of openings via which the actual injection process takes place, the combustion process is decisively influenced by an amount of “nozzle tip protrusion”. This is a measure of how far a forwardmost part of the injector, the nozzle tip, projects into the cylinder. However, different amounts of tip protrusion would be regarded as the optimum, depending on the cycle and the associated different operating points. This is due, on the one hand, to different requirements of the injection and combustion process (e.g. partial load or full load) and, on the other hand, to the fact that a large tip protrusion entails increased thermal stress on the nozzle tip at full load, reducing the life thereof, whereas this is a fairly minor problem at partial load.
The efficiency of the combustion process is determined by optimum mixture preparation, which, on the one hand, is achieved in terms of air involved by means of appropriate inlet ports and piston recess geometries and, on the other hand, in terms of the fuel involved by means of optimum introduction of the fuel through appropriate injection nozzle configuration. It should be noted here that the penetration depth (nozzle tip protrusion) of the injection nozzle is set in an optimum manner in accordance with the operating point. Low-load operating points at a relatively low engine speed, generally with a late injection event and a low injection pressure, require larger amounts of tip protrusion to achieve an optimum jet pattern in the combustion recess. With increasing load and engine speed and corresponding advance of the main injection event and increasing injection pressure, smaller amounts of nozzle tip protrusion are required to achieve a corresponding recess jet pattern. Injection jets outside the recess should be avoided for reasons connected with emissions (high HC, CO, soot figures).
In practice, the nozzle tip protrusion is chosen in such a way that it corresponds to a compromise. The nozzle tip protrusion is often adjusted by means of a rigid washer placed between the injector and the cylinder head, wherein a shoulder of the injector is supported on the washer, which, for its part, is supported on the cylinder head.
DE 40 22 299 C2 shows a height-adjustable washer having two washer parts lying one above the other and having contact surfaces which are embodied as rising helical surfaces, each having a ramp. In this case, at least two concentric helical surfaces are formed on each washer part, the ramps of said surfaces being offset relative to one another by a certain angle in the circumferential direction. The height of the washer was adjusted by twisting the washer parts relative to one another, wherein improved tilt stability of the washer parts relative to one another is achieved by means of the mutually offset ramps.
U.S. Pat. No. 7,703,727 B2 discloses an adjustable spacer arrangement having two wedge elements resting one upon the other, which are connected by at least one adjustable connecting arrangement. The latter is connected to the two wedge elements so as to be pivotable in all cases and engages with said elements via connecting elements, the spacing of which relative to one another can be varied. Varying the spacing has the effect that the wedge elements move relative to one another along their contact surface, thereby changing the overall height of the arrangement. According to one embodiment, the spacing can be varied by means of a hydraulic cylinder.
CN 202114508 U shows a height-adjustable supporting unit. This comprises a base, an adjusting block and a nut. The adjusting block and the nut are provided with internal threads and are screwed onto an external thread on a shaft of the base. The overall height of the unit can be varied by screwing and unscrewing.
In view of the prior art indicated, there is still room for improvement in the provision of an injector which is optimized as regards the injection process, especially in respect of the nozzle tip protrusion.
It is the underlying object of the present disclosure to optimize the injection process of an injector in an internal combustion engine, e.g. a diesel engine.
According to the present disclosure, the object is achieved by an injector arrangement for an internal combustion engine, comprising: an injector at least partially arranged in a cylinder head; a nozzle tip coupled to the injector and arranged at an end of the injector in an axial direction; and an actuator configured to vary a position of the nozzle tip relative to the cylinder head in the axial direction, with a minimum position and a maximum position of the nozzle tip set by the actuator.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.
FIGS. 1-4 are shown to scale, though other relative dimensions may be used.